For development of photopolymerizable compositions, organic solvents have hitherto been employed as developers, but organic solvents are, in general, expensive, poisonous, and combustible. Moreover, use of organic solvents entails high cost for countermeasures against health in working environment and environmental pollution. Therefore, it has been strongly desired to obtain a photopolymerizable composition that is developable without using such organic solvents. To this effect, it is noted that solubility and other properties of photopolymerizable compositions generally depend on the kind of binders used in the compositions.
Representative publications describing alkalidevelopable photopolymerizable compositions are set forth below. Examples of the binders whose use is described in these publications are shown in parentheses, since the main properties of the compositions are predominantly decided by the binders used therein.
Japanese Patent Publication No. 34327/79 (corresponding to U.S. Pat. No. 3,804,631) PA1 Japanese Patent Publication No. 38961/80 (corresponding to U.S. Pat. No. 3,887,450) PA1 Japanese Patent Publication No. 25957/79 PA1 Japanese Patent Application (OPI) No. 99810/77 (the term "OPI" herein used refers to a "published unexamined application") PA1 Japanese Patent Publication No. 12577/83 PA1 Japanese Patent Publication No. 6210/80
(methyl methacrylate/2-ethylhexyl methacrylate/methacrylic acid terpolymer) PA2 (styrene/mono-n-butyl maleate copolymer) PA2 (styrene/methyl methacrylate/ethyl acrylate/methacrylic acid tetrapolymer) PA2 (benzyl methacrylate/methacrylic acid copolymer) PA2 (acrylonitrile/2-ethylhexyl methacrylate/methacrylic acid terpolymer) PA2 (methyl methacrylate/ethyl acrylate/acrylic acid terpolymer, and isopropanol-partially esterified styrene/maleic anhydride copolymer)
Photopolymerizable compositions are used for various purposes as in, e.g., lithographic printing plates, resin letterpress plates, photomasks, photosensitive dry film resists, and the like. The photosensitive dry film resists comprise a film support having provided thereon a photoresist layer (hereinafter referred to as photosensitive layer) and a protective layer, as described in Japanese Patent Publication No. 25231/70 (corresponding to U.S. Patent 3,469,982).
The photosensitive dry film resist is used in the production of printed circuit boards. That is, after the protective film is stripped, the photosensitive layer is laminated on a copper-clad base under heat and pressure. The laminate is then imagewise exposed to light through a negative original in contact with the film support. The film support is removed, and the unexposed areas are removed (developed) by a developing solution, to thereby obtain a resist image on the copper surface. Then, the copper surface covered with the resist is protected by the following etching step (dissolving and removing the copper surface) and plating step (depositing solder, copper, etc. on the copper surface). Thereafter, the resist image is peeled off, and if necessary, the base surface is further subjected to etching, to thereby produce a printed circuit board.
The photosensitive layer is classified into the so-called alkali-developable type that the unexposed areas can be removed (developed) by an alkali aqueous solution and the so-called solvent-developable type that the unexposed areas can be removed by an organic solvent. Attention has recently been directed to the former alkalidevelopable type because of safety and health in the working environment and low cost for the treatment.
However, the alkali-developable photosensitive dry film resists using the aforesaid conventional binders have many problems in performance in spite of their advantages. Specifically, the resist image lines have poor resolving power and lacks faithful reproducibility of original lines; the edges of the resist image are not sharp; and the tenting strength is low. These disadvantages are attributed to the fact that conventional known photosensitive layers cannot provide a resist image having sufficient resistance to a developing solution; that the dry film resist has poor adhesion to a base; and that the photosensitive layer has insufficient solubility in the alkaline aqueous solution.